Sooner or later you will find that something is not working properly, so here are some general hints on troubleshooting, after which there are some links to more specific problems.

General Troubleshooting techniques

There are a few basic steps that can help in troubleshooting problems with KDE software. You should try these steps before asking on #kde or the kde general mailing list, since you'll probably be told to try them anyway

Try creating a new user and running your KDE software with that user. If the problem doesn't occur with the new user, there's probably a problem with a file in your ~/.kde directory (with every reference to this directory, bear in mind that some distros call it ~/.kde4). You should then try:

Rename the file causing the problem. To find an appropriate file, look in ~/.kde/share/apps/application-name or in ~/.kde/share/config/application-namerc where application-name is the name of the application you are having problems with. The config file is the most likely problem.

Clean out /tmp and /var/tmp. KDE stores some temporary files which can sometimes cause problems. You will need to be root to do this. You might also like to try removing the following files. Make sure you exit KDE first though! (The easiest safe way is to choose Failsafe at bootup.):

~/.dbus

~/.kde/tmp-hostname which is normally a symlink to the next file:

/tmp/tmp-kde-USER

~/.kde/socket-hostname which is also normally a symlink to:

/tmp/ksocket-USER

If you're running an old release from KDE, try updating to the latest version - many bugs are fixed with each new version, so your problem might already be fixed.

Try searching the Bugzilla. Many common problems have been reported and discussed there.

If your problem is more general than just one KDE application (e.g., "sound stops working when I start my KDE desktop"), try starting X with a different window manager. Even if you haven't installed another WM, 'twm' will be available, as it ships by default with X.

If you start X with the 'startx' command, just put the appropriate command in the file .xinitrc in your home directory. (If it doesn't exist, create it)